1. Field of the Invention
This invention relates to the protection of tuyeres used in refining liquid metals; more particularly, to the protection of a tuyere that is cooled by injecting a liquid cooling agent through a passageway which is disposed about the periphery of the tuyere.
2. Description of the Prior Art
It is known that a tuyere used to introduce refining substances into a liquid metal bath from beneath the surface thereof may be protected against erosion (due to heat and/or chemical reaction) by injecting fluids through passageways surrounding the central tube of the tuyere. The protective fluids may be either liquid or gaseous, but the present invention concerns only liquid protection. The liquid form of tuyere protection is exemplified by U.S. Pat. No. 3,817,744 in which there is disclosed a tuyere consisting of two concentric tubes; oxidizing gas is blown through the central tube and liquid cooling agent is injected through the annular passageway therebetween. A variety of liquids may be used as the cooling agent for such tuyeres including water, liquid hydrocarbons (e.g. fuel oil), liquid butane, liquid carbon dioxide, and others; mixtures or emulsions of liquids advantageously may be used.
It is also known, for example where liquid-protected concentric tuyeres are used for blowing oxygen into a steel-making converter from below the surface of the molten iron bath contained therein, that the pressures and flow rates of the liquid cooling agents are adjusted to give optimum tuyere wear rates but that these variables of pressure and flow rate ultimately depend on the cross-sectional area of the tuyere passageway that is available for liquid flow. Conventional tuyere construction has found this cross-sectional area to approximate 10 square millimeters or more per centimeter of mean circumference of the annular passageway available for liquid flow. Thus, for example, with such conventional concentric tuyeres operating in a steelmaking converter and being cooled with domestic fuel oil, the fuel oil flow rates range from 0.13 to 0.15 liters per minute per centimeter of mean circumference (of the annular passageway) and the pressure of the fuel oil introduced into the passageway ranges between about 4 and 8 bars. Under these conditions, which are considered normal for steelmaking operations, the rate of wear of the discharge end of the tuyere is of the order of 8 to 10 millimeters per hour of oxygen blowing.
Workers in the art have sought to achieve even better rates of wear for liquid protected tuyeres. Any improvements achieved in this regard strongly contribute to extending the life of the refractory lining in which these tuyeres are embedded and, as is well known, refractory life is an important economic factor in any metallurgical operation. The efforts of workers in the art toward this end, however, have been directed mainly at increasing the total flow of cooling agent in the annular passageway, the apparent thinking being that the more cooling agent used, the better the heat transfer characteristics of the system and thus a consequent reduction in tuyere wear. For this reason, it is not uncommon for a conventional concentric tuyere to have an annular space between the two tubes of 1 to 1.5 millimeters in order to accomodate such flow. Because the liquid cooling agent is consumed in the metallurigical operation and does not otherwise contribute to (or detract from) the chemical reactions taking place in the operation, any increase in the consumption of liquid cooling agent, particularly when it is fuel oil, is economically undesirable.